SOVIET PHYSICS JETP
VOLUME 13, NUMBER 1
JULY, 1961
TEMPERATURE DEPENDENCE OF THE HALL EFFECT IN MnAu2
V. N. NOVOGRUDSKII and I. G. FAKIDOV
Institute of Metal Physics, Academy of Sciences, U.S.S.R.
Submitted to JETP editor July 30, 1960
J. Exptl. Theoret. Phys. (U.S.S.R.) 40, 76-78 (January, 1961)
It is shown that the ordinary Hall effect in MnAu 2 is supplemented by an additional effect in
the antiferromagnetic temperature range. It is suggested that this additional effect is caused
by the presence of a high magnetic susceptibility.
MANY substances are known to exhibit more than
one form of spin ordering. The magnetic properties of these substances have been investigated
thoroughly, but their electrical properties have
been studied fully only in the case of ferromagnets.
It therefore appeared interesting to investigate the
galvomagnetic properties of antiferromagnets in
order to determine those parts of the observed
effects that are directly associated with antiferromagnetism.
We have investigated the Hall effect in the intermetallic compound MnAu 2, which is antiferromagnetic but becomes ferromagnetic in magnetic
fields above a certain threshold ( H > Hth ). 1' 2 Our
specimen exhibited the Neel temperature TN
= 92° C and Hth = 8000 oersteds. In earlier work3
we showed that the Hall emf for MnAu2 in the
region 0 < H < Hth depends linearly on the magnetic field strength H. In the present work we investigated the temperature dependence of the Hall
emf in the same specimen, using magnetic fields
in which MnAu2 remains antiferromagnetic. An
abrasive disk was used to saw the specimen from
an ingot, thus excluding large residual deformations. The emf and magnetic susceptibility were
measured as in reference 3.
The figure shows the temperature dependence
of the Hall emf for an internal magnetic field
H = 5000 oe. Curve 1 exhibits a peak located near
the Neel temperature TN, which was determined
from the temperature dependence of the magnetic
susceptibility. In this respect MnAu 2 can be contrasted with manganese telluride, where the Hall
emf falls off rapidly around the Neel temperature. 4
Let us consider the portion of the curve that
lies in the paramagnetic region. It has been shown
by Kikoin and others 5- 7 that in strongly paramagnetic substances and in ferromagnetics above the
Curie point the Hall emf can be represented by
Ex= (R 0 H + R1 yfi] ljd = R0 [I+ 4:rtot1(] Hljd,
(1)
53
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,or- _ _~--,---.--­
0
30
/00
1ao
~
•c
Temperature dependence of the Hall emf for MnA11:a with an
internal magnetic field H = 5000 oe. 1- experimental curve;
2- curve calculated from Eq. (1).
where H is the magnetic field, I is the current
flowing through the specimen, d is the thickness
of the specimen, Ro is the magnetic susceptibility,
R is the Hall constant for the ordinary effect, and
R 1 is the Hall constant for the part of the effect
that is associated with magnetization. Since it
was shown in the same investigation that R1 is
independent of temperature, we have assumed
that (1) is also valid in antiferromagnetics above
the Neel temperature. The figure shows that the
experimental curve 1 can be closely approximated
by (1) when the following numerical constants are
used:
Ro = - 2.19 x 10- 12 v-cm/amp-oe
R 1 = - 2.42 x 10-10 v-ern/amp-gauss
ot=8.8.
(2)
These values were determined by the method of
least squares from the experimental results in
the paramagnetic temperature region. It should
be noted that a = 8.8 is small compared with the
value for ferromagnetics; e.g. for very pure nickel
near the Curie point we have a ~ 10 2.
It therefore follows from the high magnetic
susceptibility of MnAu 2 ( x R; 5 x 10-3 em - 3 ) that a
considerable fraction of the Hall effect depends on
magnetization. Since it can hardly be supposed
that at temperatures below TN the parameter a
is immediately reduced to the order of unity, a
54
V. N. NOVOGRUDSKII and I. G. FAKIDOV
Hall effect resulting from a paramagnetic process
must evidently exist in the antiferromagnetic
region.
Curve 2, which represents Eq. (1) with the
values of ~ and R 1 given in Eq. (2), is seen to
agree well with the experimental curve 1 above
the Neel temperature, but to differ considerably
below that temperature. The temperature dependence of the Hall emf can therefore not be represented by (1) in the antiferromagnetic region if R 0
and R 1 are assumed to be temperature-independent. Since MnAu 2 has the electrical properties of
a metal, its conduction-electron concentration is
temperature-independent, and this must also apply
to ~- We can therefore assume that either R 1 or
a is temperature-dependent below the Neel temperature.
It should be noted that when a is of the order
of a few tens the magnetization-induced part of
the Hall effect can be appreciable only in substances where the susceptibility exceeds 10-4 em - 3•
In antiferromagnets with low susceptibility, such
as MnTe, the additional magnetization-induced
Hall emf can therefore be imperceptible.
However, the anomalous Hall effect in manganese telluride around the Neel temperature is
evidence that antiferromagnetism results in an
additional Hall emf, which is apparently produced
by a different mechanism than in MnAu 2•
1 A. J. Meyer and P. Taglang, J. Phys. Radium
17,457 (1956).
2 A. Herpin and P. Meriel, Compt. rend. 250,
1450 ( 1960).
3 1. G. Fakidov and V. N. Novogrudski'i, <PH3HKa
MeTaJlJioB H MeTaJlJ!oBeAeHHe ( Physics of Metals and
Metallography) 10, 158 (1960).
4 Uchida, Kondoh, and Fukuoka, J. Phys. Soc.
Japan 11, 27 (1956).
5 I. K. Kikoin, J. Phys. (U.S.S.R.) 9, 1 (1936).
6 Kevane, Legvold, and Spedding, Phys. Rev. 91,
1372 (1953).
7 Kikoin, Buryak, and Muromkin, Doklady Akad.
Nauk SSSR 125, 1011 (1959), Soviet Phys.-Doklady
4, 386 (1959).
Translated by I. Emin
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